what can cause hard starting on mornings and after parking for a while

Porsche made a diesel suv? wow- learn somethin' new every day- I guess "Porsche" doesn't mean what it used to- is it cold where you are? have you done a compression test? you mention a lot of stuff replaced, but have you replaced the glo plugs? you know, it's the usual drill with starting an old diesel on a cold morning- weren't you prepared for all this when you decided owning a diesel is a good idea? the accelerator pedal? really? so many questions-

You've got a VW V-6 Diesel from the Toureg suv line. Sounds as if the fuel pump is going or the check valve the maintains fuel pressure is sticking open. Check with a VW shop or if your desperate try a VW stealership. Good luck!